2 
severity and duration—the Ice Period—in which snows and 
~ glaciers spread from Greenland and Alaska southward until two- 
thirds of the continent was under snow and ice. All the region 
north of New York and Cincinnati was then changed from a para- 
dise to a howling wilderness, where not a trace remained of the 
luxuriant vegetation that before covered the surface, or of the 
varied fauna that was associated with it, except where leaves, 
trunks and bones, relics of earlier generations, were buried in 
rock or soil too deep to be reached by the grinding glacier or 
the burrowing torrent. These relics we have disinterred on 
Greenland, Disco Island, on the McKenzie and in Alaska, as 
well as’ at many places further south, in the country bordering 
the Columbia, the Missouri, in New Jersey and Virginia. Seven 
quarto volumes filled with descriptions and plates of fossil plants 
constitute the contribution that Prof. Oswald Heer has made in his 
“Flora Arctica” to our knowledge of the vegetation that covered 
the circum-polar lands before the Ice Age, and an equal mass of ma- 
terial has been gathered by Lesquereux, Ward, Fontaine and the 
writer, as a preparation for the work of illustrating the wonderfully 
rich Cretaceous and Tertiary flora of North America. Although 
but a beginning has yet been made, already the remains of at 
least a thousand distinct species of arboréscent plants have been 
brought to light. The botanical relations of many, perhaps ’ 
most of these, are yet to be accurately determined, but the gen- 
eral character of the vegetation which covered our continent in 
the later geological ages has certainly been ascertained, and 
much light has been thrown on the derivation and history of our 
present flora. 
With the facts before us, we are fully warranted in making 
the statements, that our angiosperm flora began its existence on 
this continent in middle Cretaceous times, that even then its 
present aspects were distinctly developed, and subsequent 
changes have been rather of degree than of kind. In the banish- 
ment of our Tertiary flora from the great area it once occupied, 
and its restriction to the narrow space at the South into which it 
was forced, many of its finest elements were destroyed ; and when, 
with an amelioration of climate, the exiles returned to that por- 
tion of their former home again opened to them, they came as a 
